(1) Field of the Invention
The present invention relates to a glass reflector used together with the light source for a high-voltage mercury discharge lamp and a manufacturing method therefor and more particularly to a glass reflector suitable for the light source for a projector such as a liquid crystal projector or a DLP projector and a manufacturing method therefor.
(2) Description of the Related Art
As a light source for a liquid crystal projector and a DLP projector (hereinafter, these are all referred to as a projector), in the early stage, a combination of a halogen lamp and a reflector made of heat-resisting glass such as borosilicate glass is used. However, in recent years, an HID lamp (a discharge lamp) excellent in the respects of the brightness of a projected image, a light color closer to white, and a life span of the lamp has been substituted for it. To this substitution, the progress in miniaturization and high output of a discharge lamp contributes.
Projectors, in correspondence with the spread of video instruments such as a personal computer and a DVD, are widely used from business presentation to household. Therefore, simultaneously with progress of miniaturization of a projector itself, there are increasing requests for preventing the brightness from impairment, that is, preventing a lamp from reduction in the output thereof. An increase in the output of a lamp causes an increase in the amount of heat from the lamp, and the temperature of the light source extremely rises also due to the effect of miniaturization of the projector frame, and the neck of the reflector may be at more than 600° C.
In a conventional projector, the highest temperature of the glass face is about 400 to 450° C. However, in a recent projector, the highest temperature of the glass face rises to 450 to 550° C. Therefore, as a projector, instead of a conventional reflector made of heat-resisting glass such as borosilicate glass, a reflector made of glass-ceramic glass of low thermal expansion excellent in heat resistance is widely used (for example, refer to Japanese Patent Publication 7-37334).
The reason is that there is a possibility that the rise temperature of a reflector may exceed the transformation point of borosilicate glass conventionally used and it is believed that at 550° C., a conventional reflector made of borosilicate glass has a high probability of cracking.
On the other hand, a reflector made of glass is manufactured by press-molding molten glass using a mold manufactured on the basis of a desired optical design.
Meanwhile, a reflector for a light source is required to be provided with an opening for inserting and fixing a light source lamp at the top of the reflective surface. The opening is formed by forming a neck on the rear side of the reflective surface along the optical axis of the reflector during press-molding, cutting it, and making an opening. It is well known that a reflector for a halogen lamp is punched to make an opening and then the neighborhood of the opening is rounded by a flame of a burner (refer to Japanese Utility Model Patent 2568541).
However, it is related to a reflector for a halogen lamp and not related to a reflector for a projector and the temperature of the glass surface is not increased so high.